Shure M68 mixer

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Tubetec

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Nov 18, 2015
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Just wondering if anyones repurposed the transformers from these very common units , 
They look very good quality ,mu metal sheilded , four are used as inputs and the fifth is in reverse as balanced output , 200 ohms input to hi z .
 

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It’s been a while, but I’ve used those as well as the inputs from the M-67, M-267 and M-367 in prototypes/experiments.  IIRC they are very high ratio inputs for transistor gear, something like 1:20 or 1:26 or thereabouts. People who tear up the old Akai/Roberts reel to reels seem to use them a lot, since the guy that originally started talking them up on the old Tape Op forum recommended them.

I have a post here somewhere with a Google Drive link to a bunch of response curves of mostly oddball pulls from various pieces of 60s/70s gear, and all of the above (including the M68 inputs) are in there.

They aren’t bad response-wise if I remember right, but can’t take much level as you might expect.

Edit: link to Google Drive folder:

https://drive.google.com/drive/folders/0B__Vr0ik2GcgLVlidXRjd0c2b1U?usp=sharing
 
Looking back at the M68 curve, I remembered that those were linear plots. Later, I started saving the linear and the log plots. Log plots would look pretty flat out to 20khz on that transformer.
 
Yeah, I have a shoebox full of those  bad boys!  Anywhere you need a significant step up, they work at a pinch for prototyping. I’ve even used them for line level on occasion, keeping levels (very) conservative.

If memory serves, the M68 inputs are about 1:10, M67s are 1:14 or so.
 
I’ve also used the cases as enclosures for other projects - pretty handy if the form factor works! Here’s a passive EQ using an M68 case and some of the pots & transformers (designed to plug into a mic preamp for makeup gain).
 

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;D
Monkey and 20Trees  mucho gracias for the input ,

its curious isnt it , back in the day where silicon was costly ,much of the gain lifting was done in the transformer . ,now the transformer costs hundreds of times the sillycon  :(

These transformers are probably still good for lifting dynamic mics to tube grid ( the limitations of the capsule will eclipse the bandwidth of the transformer ), 10-20 euro-bucks might be worth spending just for the cores and mu metal screens for experimentation purposes
 
Those transformers are 1:10,
they were used in the Shure Level Loc also, theres threads on the Level loc diy project around here

They're small transformers, I don't know what the specs are but they shouldn't be great. Low frequency response is probably not good and with loads of distortion in the low end
 
Whoops said:
They're small transformers, I don't know what the specs are but they shouldn't be great. Low frequency response is probably not good and with loads of distortion in the low end

I've experimented a bit with these and that's what I found. Don't put much signal in them and they're useable. Haven't found anything I can use the M68 I've got lying around yet. Not even for some "grit", as it is very noisy. Lots and lots of hiss...
 
1:10 is probably more preferable than the higher ratio units for the modern age ,
I wonder what the potting material is , looks like silicone which would probably be easy to hack apart .
They should be good enough for dynamic mics as they are ,but it would be interesting to see how they handle a guitar cab mic'd with a 58 . The quality of the Mumetal sheilds looks excellent ,you just dont find that thickness of material in the modern day ,or if you did it would cost a lot.
 
gridcurrent said:
how did you arrive at that turns ratio ?
were you in the loop with the 1:7  API 2622  ?

Just different internet sources in the past, when I was doing my DIY Level loc,
I never measured those transformers myself
 
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